A power supply device that receives an alternate-current power from an external power supply and generates a plurality of source powers has been conventionally known.
Patent Literature 1 describes a DC-DC converter including an overcurrent protection transistor that protects a switching transistor on an input side of a switching transformer from an overcurrent, in which a protection-circuit driving power for turning the overcurrent protection transistor on is generated from an electromotive force of a control winding on the input side of the switching transformer. With this configuration according to Patent Literature 1, the switching transformer is reduced in size because the switching transformer needs one winding fewer than in a case where a winding for outputting a protection-circuit driving power is provided on an output side of the switching transformer to output the protection-circuit driving power from that output-side winding.